The external ankle dorsiflexion moment can be thought of as which problem if uncontrolled during midstance?

The external ankle dorsiflexion moment can be thought of as which problem if uncontrolled during midstance?

• A. Foot slap
• B. Jackknifing
• C. Forward tibial collapse
• D. Trendelenburg

Answer: (C)

The main idea is that during midstance the ground reaction force tends to push the tibia forward, creating an external dorsiflexion moment at the ankle. To stay stable, the plantarflexor muscles must generate an opposing internal plantarflexion moment to control that forward tibial progression. If this external dorsiflexion moment is not properly countered, the tibia will move forward over the foot, causing forward tibial collapse. That’s the concept behind why forward tibial collapse is the best description. The other options refer to different problems: foot slap involves insufficient dorsiflexor control at heel strike, Trendelenburg points to hip abductor weakness and pelvis drop, and jackknifing describes a proximal (hip/knee/trunk) collapse pattern rather than an ankle-controlled midstance issue.

The main idea is that during midstance the ground reaction force tends to push the tibia forward, creating an external dorsiflexion moment at the ankle. To stay stable, the plantarflexor muscles must generate an opposing internal plantarflexion moment to control that forward tibial progression. If this external dorsiflexion moment is not properly countered, the tibia will move forward over the foot, causing forward tibial collapse.

That’s the concept behind why forward tibial collapse is the best description. The other options refer to different problems: foot slap involves insufficient dorsiflexor control at heel strike, Trendelenburg points to hip abductor weakness and pelvis drop, and jackknifing describes a proximal (hip/knee/trunk) collapse pattern rather than an ankle-controlled midstance issue.